The invention relates to flash lamps and particularly to flash lamps which are electrically activated.
Electrically-activated flash lamps as used in many photographic applications are well known in the art with examples described in U.S. Pat. Nos. 3,959,860 (Schindler), 3,941,555 (Anderson et al), and 3,897,196 (Saunders et al). Such flash lamps typically include a glass envelope having a combustion-supporting atmosphere (e.g. oxygen) therein established at a pressure of several (e.g. 5-10) atmospheres. A pair of spaced apart metallic leads are sealed within one end of the lamp and project within the envelope to provide the necessary electrical current path to the lamp's primer material. When activated, the primer ignites a quantity of combustible material (e.g. zirconium) to produce the required highly intense flash of light. In electrically-activated flash lamps of the low-voltage variety, a filament is used to bridge the projecting ends of the metallic leads, while in high-voltage flash lamps (those requiring hundreds or thousands of volts at low energy to achieve ignition), a quantity of primer material may serve as the bridge. Primer may also be applied to the aforedescribed filament in low-voltage type lamps.
As stated, flash lamps of the varieties described above typically include a pair of metallic leads which project through the lamp's glass envelope. There are several disadvantages to this requirement, including the following:
1. Sealing of the leads into the envelope is a costly production step due primarily to the high cost of equipment required to accomplish this step;
2. Use of metallic leads limits the types of glasses which can be satisfactorily used as the envelope component due to the stringent requirement to mate glass and leads having similar expansion characteristics;
3. The electrical leads must establish sound, direct contact with the respective electrical firing circuit. This requires an additional manufacturing step as well as extra material. Such a requirement also restricts the design possibilities for multi-lamp units; and
4. The amount of space and glass necessary to properly seal the metallic leads poses a serious limitation to the designing of small flash lamps.
From the above disadvantages, it is understood that an electrically-activated flash lamp which does not require metallic leads within the lamp's glass envelope would constitute a significant advancement in the art.